Bring 2 cups of water, the salt and dark brown sugar to a boil. Cook until the salt and sugar are dissolved. Turn off the heat and add in the onions, garlic, and bay leaves. Let cool to room temperature.
Stir in the rest of the water and pumpkin beer, then submerge the turkey in the brine for 12 hours.
When you're ready to cook your turkey, remove it from the brine and lightly rinse the turkey, including the cavity. Blot it dry with a paper towel and cook according to your favorite method.